TWI861162B - Light-emitting diode and fabrication method thereof - Google Patents

Abstract

The invention describes a Light-emitting diode and a manufacturing method. The invention relates to a light emitting diode (LED) comprising an active region and having a three-dimensional (3D) structure. The 3D LED comprises: a first GaN-based layer having a first content of Aluminium and a first content of Indium, and a second GaN-based layer interposed between and in contact with the first layer and the active region, having a second content of Aluminium and a second content of Indium, the second content of indium being strictly higher than the first content of indium so as to promote the formation of misfit dislocations at an interface between said first and second layers. Advantageously, the active region and the first and second layers extend along semi-polar crystallographic planes. The invention also relates to a method for manufacturing such a 3D LED.

Description

Light emitting diode and manufacturing method thereof

The present invention relates to the field of optoelectronics, and has particularly advantageous applications in the field of gallium nitride-based light-emitting diodes (diodes électroluminescentes à base de GaN) with a three-dimensional structure.

Gallium nitride (GaN)-based light emitting diodes (LEDs) are usually manufactured using a technology called planar technology, which involves forming a stack of two-dimensional (2D) layers on a substrate plane (plan de base) in a direction perpendicular to the substrate plane.

The stack generally includes a region known as the active region in which radiative recombination of electron-hole pairs occurs, which allows light radiation of the principal wavelength to be obtained.

For display applications, LEDs can be configured to emit light radiation with a dominant wavelength of blue, green, or red.

The stack is structured a posteriori, for example by a photolithography/etching step, which then allows the formation of a plurality of light-emitting diodes, each having a terrace structure. The terrace structure generally has a top and side walls. The side walls obtained by a posteriori structuring generally have defects that contribute to the appearance of a non-radiating surface complex.

In the case of micro-LEDs, for mesa sizes less than a few tens of micrometers, e.g., less than 10 μm, the surface area/volume ratio of the mesa increases and the effect of the sidewalls becomes significant. In particular, the non-radiative recombination rate of such micro-LEDs increases due to the increased fraction of recombination on the non-radiative surface. The performance of these micro-LEDs is therefore deteriorated.

Direct formation of three-dimensional (3D) structures is a promising alternative to constructing two-dimensional (2D) planar stacks in order to reduce terrace sidewall defects. This alternative allows, in particular, to significantly reduce the non-radiative surface recombination rate.

Figures 1A and 1B show such a 3D structure for manufacturing LEDs and/or micro-LEDs.

These 3D structures can be in the shape of GaN-based microfils or nanofils extending primarily in a direction perpendicular to the substrate plane.

They can be formed by epitaxial growth from a nucleation layer 12 ′ which is partially covered by a masking layer 13 .

In these embodiments, the nucleation layer 12' is two-dimensional and extends in the plane of the substrate. The growth of the 3D structure occurs through the window 130 of the masking layer 13.

These 3D structures can have different internal structures.

1A shows a first architecture, referred to as axial architecture, in which the active region 123 extends laterally in the 3D structure parallel to the substrate plane.

This axial architecture allows, in particular, the doping of a high concentration of indium (In) in the GaN-based active region 123. Such an active region 123 can emit light radiation having a wavelength of green or red.

Therefore, this axial architecture can be used to make green or red 3D micro-LEDs.

However, such structures have a low radiation yield.

Furthermore, for high concentrations of In, the distribution of In in the active region is usually not uniform in this type of axial structure.

1B shows a second architecture, called radial architecture. According to this radial architecture, the active region 123 extends along the side of the 3D structure perpendicular to the substrate plane.

This radiation architecture has good radiation yield for LEDs emitting blue light.

However, for the indium-rich radial active region 123 emitting light radiation having a wavelength greater than 500 nm, the yield decreases.

Therefore, this radial architecture is not optimal for making green or red 3D micro-LEDs.

Therefore, existing solutions for 3D structured LEDs cannot achieve large amounts of indium doping and high radiation yield.

The present invention aims to at least partially overcome some of the above-mentioned disadvantages.

In particular, an object of the present invention is to provide a GaN-based 3D structured light emitting diode (LED) which allows high levels of indium to be doped in the active region while maintaining or even improving the radiation yield.

Another object of the present invention is to provide a GaN-based 3D structure light emitting diode (LED) in which the distribution of indium is uniform.

Another object of the present invention is to provide a method for manufacturing such a 3DGaN-based LED.

Other objects, features and advantages of the present invention will become apparent by studying the following description and drawings. It should be understood that other advantages can be combined.

To achieve the above object, according to a first aspect of the present invention, a light emitting diode (LED) is provided, which has a GaN-based three-dimensional (3D) structure and includes an active region based on indium gallium nitride (InGaN) for emitting light radiation. The three-dimensional (3D) structure is a linear shape with a pyramidal top (the 3D structure is called a 3D pen-like structure) or a pyramid shape (the 3D structure is called a 3D pyramid structure).

The light-emitting diode further comprises:

- a GaN-based GaN-based first layer having a first content of aluminum and a first content of indium, and

-A second GaN-based layer, which is disposed between and in contact with the first layer and the active region, and has a second content of aluminum and a second content of indium.

The second content of indium may advantageously be strictly greater than the first content of indium, so that a dislocation of lattice parameter mismatch is formed at the interface between the first layer and the second layer.

The active region, the first layer and the second layer may advantageously extend along semipolar crystal planes.

The improvements of the present invention make it possible to determine the following points:

- Indium doping in the active region depends inter alia on the polarity of the layers forming the active region and on the control of mechanical stresses in the 3D structure,

- The radiation recombination rate and thus the radiation yield depend in part on the strength of the piezoelectric field induced in the InGaN-based active region. This piezoelectric field also depends on the polarity of the layers forming the active region.

Existing solutions for 3D structured LEDs do not seem to be able to effectively control the doping of indium, the appearance of mechanical stress, and the intensity of the piezoelectric field.

In the case of the axial configuration (FIG. 1A), the active region is formed on a polar plane (plane c or -c of the hexagonal crystal structure of the GaN-based material, as shown in FIG. 2A), which induces a strong piezoelectric field within the active region.

This strong electric field produces a spatial separation of charge carriers (electrons and holes). This separation of carriers greatly reduces the electron-hole recombination rate. The internal quantum efficiency IQE and radiation yield are low.

The polar planes of the axial structure allow relatively large amounts of In doping into the active region.

However, by increasing the concentration of indium [In]a in the active region, for example [In]a>17%, the InGaN-based material in the active region is subjected to increasing mechanical stress. Therefore, structural defects can be formed by plastic stress relaxation in the active region. This reduces the IQE efficiency and radiation yield of the active region. The increase in mechanical stress and/or plastic relaxation further promotes the uneven distribution of indium in the active region.

In the case of a radial architecture (FIG. 1B), the active region is formed on a non-polar plane (plane a or m of the hexagonal crystal structure of the GaN-based material, as shown in FIG. 2B).

Plastic stress relaxation in nonpolar planes occurs earlier than in polar planes. This crystal orientation promotes the appearance of crystal defects. These crystal defects, especially stacking faults, form in the active region and grow rapidly.

In order to minimize the intensity of the piezoelectric field and optimize the doping of indium in the active region, the present invention provides for forming the active region on a semi-polar plane, as shown in Figures 1C and 2C. This architecture is referred to as a pyramid architecture hereinafter.

Unlike polar planes, the piezoelectric field of semi-polar planes is weak or zero. According to one embodiment, the semi-polar planes are preferably of the {10-11} type (FIG. 2C) and have a piezoelectric field that is virtually zero.

The internal quantum efficiency IQE of the pyramid architecture is therefore improved compared to the axial architecture.

The stability of the emission of optical radiation at the dominant wavelength is also improved over a wider range of current densities.

Semipolar planes also allow for greater amounts of indium to be doped than nonpolar planes.

This pyramidal structure also improves indium doping compared to the radial structure.

In addition, in order to effectively release the mechanical stress at the active region, the present invention provides a first layer of GaN-based and a second layer of GaN-based that are respectively poor in indium and rich in indium in a 3D structure parallel to the semipolar plane. These first and second layers are also referred to as "stress relaxation structures" hereinafter.

The difference in lattice parameters between the first layer and the second layer allows for the generation of lattice parameter mismatched dislocations at the interface between the first layer and the second layer, often referred to as "misfit dislocations".

The appearance of misfit dislocation (MD) corresponds to the plastic relaxation of the first and second layers.

The stress-relaxed structure thus allows the formation of active regions on the relaxed GaN-based material.

Therefore, the content of indium doped in the active region can be increased by minimizing the density of structural defects in the active region.

Furthermore, the uniformity of the indium distribution within the at least partially relaxed active region is improved.

Preferably, the first layer and the second layer are also aluminum-rich (Ga(In)AlN) and aluminum-poor (Ga(Al)InN), respectively. The addition of aluminum makes the lattice parameter difference between the first layer and the second layer more pronounced. Therefore, it is not necessary to form an indium-rich second layer to obtain the lattice parameter difference required for the appearance of MD. This allows preventing the second layer, which has a too high indium content, from absorbing light radiation.

Under the synergistic effect, the misfit dislocations generated by the stress relaxation structure are confined within the semipolar planes of the pyramid structure.

Therefore, unlike structural defects generated in polar or nonpolar planes, misfit dislocations do not propagate into the active region.

The necessary distance d between the interface and the active region can be minimized to avoid the influence parasite of misfit dislocations on the operation of the active region, especially on the spatial charge region formed at the active region.

Therefore, the limitation of misfit dislocations at the interface allows limiting the thickness of the second layer to a thickness less than 150 nm, for example between 10 nm and 150 nm.

Thus, this integrated stress relaxation structure of the pyramid architecture allows effective control of mechanical stresses. Other advantages associated with this improved stress control are described in detail below. This improvement in stress control generally improves the IQE.

Therefore, LEDs based on the pyramid architecture with a stress-relaxed structure have a higher radiation yield, especially for configurations emitting green or red light radiation.

A second aspect of the present invention relates to a method of manufacturing a gallium nitride (GaN)-based light emitting diode (LED) having a three-dimensional (3D) structure, the diode including an InGaN-based active region for emitting light radiation.

The method comprises the following steps:

- providing a three-dimensional structure on a substrate, comprising at least one GaN-based surface layer, said surface layer extending along a semipolar crystal plane,

- forming a GaN-based first layer on the surface layer, the GaN-based first layer extending along the semipolar crystal plane and having a first content of aluminum and a first content of indium,

- forming a GaN-based second layer directly on the first layer, the GaN-based second layer extending along the semipolar crystal plane and having a second content of aluminum and a second content of indium, and making the second content of indium strictly higher than the first content of indium, thereby forming a lattice parameter mismatch dislocation at the interface between the first layer and the second layer,

- forming an InGaN-based active region directly on the second layer extending along the semipolar crystal plane.

Before starting to discuss the embodiments of the present invention in detail, it should be remembered that, according to the first aspect of the present invention, the present invention particularly includes the following optional features, which can be used in combination or alternatively.

According to one embodiment, the first content and/or the second content of aluminum is zero.

According to one embodiment, the first content of indium is strictly less than the first content of aluminum.

According to one embodiment, the first content of indium is non-zero.

According to one embodiment, the second content of indium is strictly higher than the second content of aluminum.

According to one embodiment, the first content [In] ₁ of indium is 0% to 10%.

According to one embodiment, the second content of indium [In] ₂ is 3% to 25%.

According to one embodiment, the first content of aluminum [Al] ₁ is 0% to 35%.

According to one embodiment, the second content of aluminum [Al] ₂ is 0 to 10%.

According to one embodiment, the interface is located at a distance d from the active region such that d>10 nm.

According to one embodiment, the semipolar crystal plane is of the {10-11} type.

According to one embodiment, the LED is configured to emit light radiation having a wavelength of 500 nm to 650 nm.

According to one embodiment, the three-dimensional structure is referred to as a three-dimensional pencil structure and is in the shape of a wire with a conical top.

According to one embodiment, the three-dimensional structure is called a three-dimensional pyramid structure and is in the shape of a pyramid.

According to one embodiment, a three-dimensional structure is formed from a planar substrate.

According to one embodiment, a three-dimensional structure is formed from a three-dimensional substrate having a textured surface.

According to one embodiment, the substrate is based on a material selected from silicon, GaN, sapphire.

According to the second aspect of the present invention, the present invention particularly comprises the following optional features, which can be used in combination or in substitution:

According to one embodiment, the formation of the first and second layers and the active region is performed by molecular beam epitaxy (MBE).

According to one embodiment, the formation of the first and second layers and the active region is performed on a three-dimensional substrate having a textured surface.

According to one embodiment, the formation of the active region is performed at least in part at a temperature greater than 550°C.

In the present invention, the formation of a stress relaxation structure based on a pyramid structure is particularly used for the manufacture of 3D LEDs.

The present invention can be more broadly applied to various optoelectronic devices having a 3D structure including an active region.

The active region of an optoelectronic device refers to the region from which most of the optical radiation provided by the device is emitted, or the region from which most of the optical radiation received by the device is captured.

Therefore, the present invention can also be implemented in the context of laser or photovoltaic devices.

Unless explicitly mentioned otherwise, in the context of the present invention, the relative arrangement of a third layer between the first layer and the second layer does not necessarily mean that these layers are in direct contact with each other, but rather means that the third layer is either in direct contact with the first layer and the second layer, or is separated from the first layer and the second layer by at least one other layer or at least one other element.

The steps of forming the different layers and regions should be understood in a broad sense: they can be performed in several sub-steps that are not necessarily strictly consecutive.

In the present invention, the types of doping are indicated. These dopings are non-limiting embodiments. The present invention covers all embodiments with the opposite doping. Thus, if an exemplary embodiment mentions P doping for the first region and N doping for the second region, then the present specification at least implicitly describes the opposite embodiment, where the first region has N doping and the second region has P doping.

The doping referred to as P includes all dopings with positive charge carriers, regardless of the concentration of the dopant. Therefore, P doping can be understood as P, P+, or P++ doping. Similarly, the doping referred to as N includes all dopings with negative charge carriers, regardless of the concentration of the dopant. Therefore, N doping can be understood as N, N+, or N+ doping.

The dopant concentration ranges associated with these different dopings are as follows:

P++ or N++ doping: greater than 1×10 ²⁰ cm ^-3

P+ or N+ doping: 5×10 ¹⁸ cm ^-3 to 9×10 ¹⁹ cm ^-3

P or N doping: 1×10 ¹⁷ cm ^-3 to 5×10 ¹⁸ cm ^-3

Intrinsic doping: 1×10 ¹⁵ cm ^-3 to 1×10 ¹⁷ cm ^-3 .

In the following, the following abbreviations related to material M are optional:

Based on the terminology commonly used in the field of microelectronics with the suffix -i, M-i refers to the material M that is either intrinsically doped or unintentionally doped.

Based on the terminology commonly used in the field of microelectronics with the suffix -n, M-n refers to a material M with N, N+, or N++ doping.

Based on the terminology commonly used in the field of microelectronics with the suffix -p, M-p refers to a material M with P, P+, or P++ doping.

In this patent application, the terms "concentration" and "content" are synonymous.

More specifically, concentration may be expressed in relative units, such as mole fraction or atomic fraction, or in absolute units, such as atoms per cubic centimeter (cm ^-3 ).

Hereinafter, unless otherwise stated, concentrations are expressed as atomic fractions in atomic percent.

In this patent application, the terms "light emitting diode", "LED" or simply "diode" are synonymous. "LED" may also be understood as "micro-LED".

A substrate, layer, or device "based on" a material M refers to a substrate, layer, or device that contains only the material M or contains the material M and optionally other materials (e.g., alloying elements, impurities, or doping elements). Thus, a gallium nitride (GaN)-based LED may, for example, include gallium nitride (GaN or GaN-i) or doped gallium nitride (GaN-p, GaN-n), or gallium indium nitride (InGaN), gallium aluminum nitride (AlGaN), or gallium nitride with different aluminum and indium contents (GaInAlN). In the context of the present invention, the material M is typically crystalline.

In this patent application, the thickness of the layer and the height of the device will be given priority. The thickness is obtained in a direction perpendicular to the main extension plane of the layer and the height is obtained in a direction perpendicular to the substrate plane of the substrate.

The terms "substantially," "approximately," and "approximately" mean, when they refer to a value, "within 10% of that value," or when they refer to an angular direction, "within 10% of that direction." Thus, a direction substantially perpendicular to a plane means a direction that is at an angle of 90°±10° relative to the plane.

To determine the geometry of the LED, the crystal orientation and the composition of the different layers, scanning electron microscopy (SEM) or transmission electron microscopy (TEM) or scanning transmission electron microscopy (STEM) can be performed.

Microdiffraction in TEM can determine the crystal orientation of different layers and regions.

TEM or STEM are also very suitable for observing and identifying structural defects, especially misfit dislocations. Different techniques are implemented in a non-exhaustive manner below: imaging in dark field and bright field, imaging in weak beam, imaging in high-angle HAADF (short for "high-angle annular dark field") diffraction.

The chemical composition of different layers or regions can be determined using the well-known EDX or X-EDS method, which is an abbreviation of "Energy Dispersive X-ray Spectroscopy", which stands for "Energy Dispersive Analysis of X-ray Photons".

This method is very suitable for analyzing the composition of small devices, such as 3D LEDs. It can be performed on metallographic cross-sections using a scanning electron microscope (SEM) or on thin sections using a transmission electron microscope.

In particular, as described in the present invention, all these techniques allow determining whether an optoelectronic device with a 3D structure includes a stress-relaxed structure according to a semipolar plane.

A first embodiment of an LED according to the present invention will now be described with reference to FIGS. 3A to 3D .

For the sake of clarity, the following description is based on a single basic 3D structure constituting a 3D LED. It should be understood that a 3D LED may include multiple adjacent basic 3D structures distributed on the same substrate. Other basic 3D structures in the multiple basic 3D structures are considered to be substantially the same as the basic 3D structure described below.

The basic 3D structure obtained according to this first embodiment is a GaN-based pyramid.

In a first step, a pyramid-shaped support structure 12 is formed ( FIG. 3A ).

The side faces of the pyramidal support structures 12 are oriented in the semipolar planes of the hexagonal crystal structure whose c-axis is perpendicular to the base plane.

According to one embodiment, they may have an angle of about 80° relative to the substrate plane, corresponding approximately to semipolar planes of the {20-21} type.

According to another embodiment, they may have an angle of about 60° relative to the substrate plane, corresponding approximately to a semipolar plane of the {10-11} type.

The support structure 12 may be made of GaN-based materials.

Such a structure may be obtained from a planar substrate 11, for example made of silicon or sapphire, which is optionally provided with a GaN-based nucleation layer (not shown).

A masking layer comprising windows, for example made of silicon nitride Si3N4, can allow local growth of GaN-based materials. These windows typically have dimensions, such as diameter or average diameter, between 50 nm and 30 μm. The distance between two windows can be between 100 nm and 10 μm. These windows can be made by UV or DUV (abbreviation for deep ultraviolet) lithography or electron beam lithography.

According to one possibility, the support structure 12 grows through a window in the masking layer. Thus, the diameter of the base of the support structure 12 is substantially equal to the diameter of the corresponding window.

The growth of GaN-based materials can be accomplished by molecular beam epitaxy MBE, vapor phase epitaxy HVPE (abbreviation for "Hydrogen Vapor Phase Epitaxy") using chlorinated gas precursors, chemical vapor deposition CVD and MOCVD (abbreviation for "Metal Organic Chemical Vapor Deposition"), vapor phase epitaxy MOVPE (abbreviation for "Metal Organic Vapor Phase Epitaxy") using organometallic precursors. Optionally, conventional surface preparation steps (chemical cleaning, heat treatment) can be performed prior to growth.

Thus, germination islands can appear at the window of the masking layer at the beginning of growth and develop into a pyramidal shape during growth, depending on the growth conditions. In particular, growth conditions in which the ratio of V/III elements, typically the ratio of Ga/N, is greater than or equal to 100 promote the growth of these islands into a pyramidal shape.

Thus, a GaN-based pyramid-shaped support structure 12 is obtained ( FIG. 3A ).

According to one embodiment, the GaN-based material of the support structure 12 may be an InGaN alloy, which is commonly used to manufacture green or red LEDs.

However, this massive InGaN support structure 12 has significant absorption at emission wavelengths of green or red radiation.

The present invention provides a stress relaxation structure that allows overcoming the use of bulk InGaN support structures that are typically required for subsequently formed InGaN-based active regions.

Therefore, preferably, the GaN-based material of the support structure 12 can be made of bulk GaN. Therefore, the absorption of the light radiation emitted by the LED by the support structure 12 is greatly reduced. The yield of the LED can be improved.

According to another embodiment, the GaN-based material of the support structure 12 may be an AlGa(In)N alloy having an aluminum content greater than an indium content.

Optionally, the substrate 11 can be textured in turn, thereby forming pyramid islands on the surface.

In this case, a thin layer of GaN or InGaN can be deposited on these pyramid islands to form a support structure 12.

In this case, the support structure 12 may consist essentially of a substrate material (eg, silicon) and a thin GaN base layer disposed on top of the material.

The support structure 12 may include an N-doped GaN-based region. The N-doped region may be formed in a known manner by growth, implantation and/or activation annealing. The N-doping may in particular be obtained directly from a silicon or germanium source during growth, for example by adding silane or disilane or germanium vapor.

Then, a first layer 121 of a stress relaxation structure may be formed in a second step ( FIG. 3B ).

It is based on GaAl(In)N, preferably based on GaAlN.

The concentration [In] ₁ of indium in the first layer 121 may be between 0% and 10%.

The aluminum concentration [Al] ₁ of the first layer 121 may be between 0% and 35%.

The thickness of the first layer 121 is preferably between 10 nm and 150 nm.

Then, in the third step, a second layer 122 of a stress relaxation structure is formed so as to be in direct contact with the first layer 121 ( FIG. 3C ).

It is based on GaIn(Al)N, preferably GaInN.

The indium concentration [In] ₂ of the second layer 122 may be 3% to 25%.

The aluminum concentration [Al] ₂ of the second layer 122 may be 0% to 10%.

The thickness of the second layer 122 is preferably 10 nm to 150 nm.

The respective concentrations [In] ₁ , [In] ₂ , [Al] ₁ , [Al] ₂ are selected to generate a misfit dislocation at the interface 1221 between the first layer 121 and the second layer 122 while minimizing absorption of light radiation emitted by the LED by the first layer 121 and the second layer 122 .

According to one embodiment, the concentrations of aluminum [Al] ₁ and [Al] ₂ are zero, and the concentrations of indium [In] ₁ and [In] ₂ satisfy [In] ₂ > [In] ₁ , preferably [In] ₂ - [In] ₁ > 10%.

According to another embodiment, the aluminum concentrations [Al] ₁ and [Al] ₂ are not zero, and it is verified that [Al] ₁ /([In] ₁ +[Al] ₁ ) ≥ 0.8 and [In] ₂ /([In] ₂ +[Al] ₂ ) ≥ 0.2.

For given indium concentrations [In] ₁ and [In] ₂ , a non-zero aluminum [Al] ₁ concentration can accentuate the difference in lattice parameters between the first layer 121 and the second layer 122. This therefore allows the indium concentration [In] ₂ to be reduced while maintaining the formation of misfit dislocations at the interface 1221 between the first layer 121 and the second layer 122.

The relative reduction of the indium concentration [In] ₂ allows limiting the absorption of the second layer 122.

The first layer 121 and the second layer 122 can be formed by molecular beam epitaxy MBE, vapor phase epitaxy HVPE (abbreviation of “Hydrogen Vapor Phase Epitaxy”) using a chlorinated gas precursor, chemical vapor deposition CVD and MOCVD (abbreviation of “Metal Organic Chemical Vapor Deposition”), vapor phase epitaxy MOVPE (abbreviation of “Metal Organic Vapor Phase Epitaxy”) using an organic metal precursor.

The stress-relaxed structure allows a better distribution of the stress budget in different layers and regions of the 3D structure of the LED. Therefore, it is particularly advantageous in the case of a good design of the stresses during the design of LEDs or optoelectronic devices.

The stress-relaxed structure allows, for example, a uniform distribution of stress in the 3D structure of an LED. Thus, the uniformity of the indium distribution in different layers and regions of the 3D structure can be improved.

The structure also has the purpose of forming a second InGaN base layer 122 at least on the upper part of this layer 122, the second InGaN base layer 122 having a low or zero residual stress level.

In particular, this structure allows confinement of misfit dislocations at the interface 1221, depending on the specific orientation of the semipolar planes. The upper portion of layer 122 is preserved. It has few or no structural defects.

The next step is to form an InGaN-based active region 123 in this upper part of layer 122 ( FIG. 3D ).

The active area 123 may be formed by the same epitaxy or deposition technique used to form the first layer 121 and the second layer 122. They may in particular be formed in the same growth frame.

The active region 123 may include alternating InGaN quantum wells and GaN or AlGaN wells in a known manner.

The active region 123 is grown by epitaxial growth on the partially or fully relaxed layer 122.

The crystal quality of region 123 is thus improved.

The distribution of indium in the quantum wells of the active region 123 also has better uniformity.

Therefore, the indium content of the quantum wells of the active region 123 can be increased while maintaining good crystal quality and good uniformity of indium distribution.

Therefore, the growth temperature of high indium content quantum wells can be increased. In particular, a growth temperature of about 550°C or higher can be used. This also facilitates obtaining InGaN-based quantum wells with good crystal quality.

The thickness of the InGaN quantum well can also be increased without exceeding the total permissible stress budget. This allows the Auger losses in the active region 123 to be limited.

The radiation yield is thus increased.

A layer of a P-doped GaN-based region may then be deposited on the active region 123 to complete the structure of the 3D LED. The P-doped region may be produced by growth, implantation and/or activation annealing in a known manner.

A second embodiment of an LED according to the present invention is shown in FIGS. 4A to 4D .

The following only describes the distinguishing features of the second embodiment relative to the first embodiment, and the other features are considered to be the same as those of the first embodiment.

The basic 3DGaN-based structure obtained according to the second embodiment is a pencil-like structure, and is in the shape of a wire with a tapered top.

Only the morphology of the 3D structure of the second embodiment is different from the 3D structure of the first embodiment.

The pencil-shaped supporting structure 12 ( FIG. 4A ) formed in the first step includes a base portion 12 a and a top portion 12 b.

The side surface of the base 12a is substantially oriented along the c-axis of the hexagonal crystal structure, perpendicular to the base plane.

The side surfaces of the top portion 12b are oriented along the semipolar planes of the hexagonal crystal structure.

Then, a first layer 121, a second layer 122, and an active region 123 are formed on the side surfaces of the base portion 12a and the side surfaces of the top portion 12b (FIGS. 4B-4D).

The steps of forming the different layers 121, 122 and region 123 of the first embodiment may be applied to the second embodiment with appropriate modifications.

Specifically, the formation of the first layer 121 includes a portion 121a formed on the side of the base 12a, and a portion 121b formed on the side of the top 12b. The portions 121a and 121b of the first layer 121 are continuous (FIG. 4B).

In particular, the formation of the second layer 122 includes forming a portion 122a on the portion 121a and forming a portion 122b on the portion 121b. The portions 122a and 122b of the second layer 122 are continuous (FIG. 4C). The portions 121b, 122b form a stress relaxation structure equivalent to the first embodiment. The interface 1221b between the portions 121b, 122b is equivalent to the interface 1221 described and shown in the first embodiment. In particular, it allows limiting the misfit dislocation generated by the stress relaxation structure including the portions 121b, 122b.

Specifically, the formation of the active region 123 includes forming a portion 123a on the portion 122a and forming a portion 123b on the portion 122b. The portions 123a and 123b of the active region 123 are continuous (FIG. 4D).

Due to the respective orientation of the portions 121a, 122a, 123a on the one hand and the respective orientation of the portions 121b, 122b, 123b on the other hand, the composition of the first layer 121 and the second layer 122 as well as the active area 123 may vary depending on the plurality of portions.

In particular, the indium concentration of portions 121a, 122a, 123a is lower than the indium concentration of portions 121b, 122b, 123b, respectively. On the contrary, in appropriate cases, the aluminum concentration of portions 121a, 122a, 123a is substantially equal to the aluminum concentration of portions 121b, 122b, 123b. Therefore, the electrical injection of electric carriers is preferably completed at portions 121b, 122b, 123b. Therefore, the operation of the optoelectronic device based on the pencil-shaped support structure 12 described in this second embodiment is similar to the operation of the optoelectronic device based on the pyramid-shaped support structure 12 described in the first embodiment. The advantages mentioned in the first embodiment are also valid for the second embodiment.

The present invention also relates to a method for manufacturing a 3D LED as described by the aforementioned exemplary embodiments.

The present invention is not limited to the aforementioned embodiments, but extends to all embodiments covered by the claims.

11: substrate 12: support structure 12’: nucleation layer 12a: base 12b: top 121: first layer 1221: interface 122: second layer 123: active region 13: shielding layer 130: window

The objects, subjects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments shown in the drawings, in which:

- FIG. 1A shows a 3D LED structure with an axial architecture according to the prior art.

- Figure 1B shows a 3D LED structure with a radial architecture according to the prior art.

- Figure 1C shows a 3D LED structure with a pyramid architecture according to an embodiment of the present invention.

- Figure 2A shows a c-type polar plane with a hexagonal crystal structure.

- Figure 2B shows the non-polar a-plane and m-plane of the hexagonal crystal structure.

- Figure 2C shows a {10-11} type semipolar plane with a hexagonal crystal structure.

- Figures 3A to 3D show the steps of manufacturing a 3D LED with a pyramid structure according to an embodiment of the present invention.

- Figures 4A to 4D show the steps of manufacturing a 3D LED with a pyramid structure according to another embodiment of the present invention.

The illustrations are given by way of example and do not limit the present invention. They constitute schematic diagrams of principles intended to facilitate understanding of the present invention and are not necessarily within the scope of actual application. In particular, the dimensions of the different layers and regions of the 3D LED do not represent actual dimensions.

12’: Nucleation layer

13: Masking layer

123: Active area

Claims (13)

A gallium nitride (GaN)-based light emitting diode (LED) having a three-dimensional (3D) structure and comprising an InGaN-based active region (123) for emitting light radiation, wherein the three-dimensional structure (3D) is a line shape or a pyramid shape having a conical top, wherein the diode is characterized in that it further comprises: - a GaN-based first layer (121) having a first content [Al] ₁ of aluminum and a first content [In] ₁ of indium, and - a GaN-based second layer (122) disposed between the first layer (121) and the active region (123) and in contact with them, wherein the second layer (122) has a second content [Al] ₂ of aluminum and a second content [In] 1 of indium. ₂ , the second content of indium is strictly greater than the first content of indium, so that a dislocation of lattice parameter mismatch is formed at an interface (1221) between the first and second layers (121, 122), and the active region (123) and the first and second layers (121, 122) extend along a semipolar crystal plane, wherein the contents of aluminum [Al] ₁ and [Al] ₂ are not zero, and it is verified that [Al] ₁ /([In] ₁ +[Al] ₁ )

0.8 and [In] _2/ ([In] ₂ + [Al] ₂ )

0.2. The LED according to claim 1, wherein the first content of indium is strictly less than the first content of aluminum, and the second content of indium is strictly higher than the second content of aluminum. An LED according to claim 1 or 2, wherein the first indium content [In] ₁ is 0% to 10%. An LED according to claim 1 or 2, wherein the second indium content [In] ₂ is 3% to 25%. An LED according to claim 1 or 2, wherein the first aluminum content [Al] ₁ is greater than 0% and less than or equal to 35%. An LED according to claim 1 or 2, wherein the second aluminum content [Al] ₂ is greater than 0% and less than or equal to 10%. An LED according to claim 1 or 2, wherein the interface (1221) is located at a distance d from the active region (123), wherein d>10nm. The LED according to claim 1 or 2, wherein the semipolar crystal plane is of the {10-11} type. The LED according to claim 1 or 2 is configured to emit light radiation with a wavelength of 500nm to 650nm. An LED according to claim 1 or 2, wherein the three-dimensional structure is formed from a three-dimensional substrate (11) having a textured surface. According to the LED of claim 10, the three-dimensional substrate (11) is based on a material selected from silicon, gallium nitride, and sapphire. A method for manufacturing a GaN-based light emitting diode (LED) having a three-dimensional (3D) structure, the diode comprising a GaN-based active region (123) for emitting light radiation, the method comprising the following steps: - providing a three-dimensional structure comprising at least one GaN-based surface layer on a substrate, the surface layer extending along a semipolar crystal plane, - forming a GaN-based first layer (121) on the surface layer, the GaN-based first layer extending along the semipolar crystal plane and having a first content [Al] of ₁ aluminum and a first content [In] of ₁ indium, - directly forming a GaN-based second layer (122) on the first layer (121), the GaN-based second layer extending along the semipolar crystal plane and having a second content [Al] of ₂ aluminum and a second content [In] of 1 indium, ₂ of indium, so that the second content of indium is strictly higher than the first content of indium, wherein the contents of aluminum [Al] ₁ and [Al] ₂ are not zero, and verifying that [Al] ₁ /([In] ₁ +[Al] ₁ )

0.8 and [In] ₂ /([In] ₂ +[Al] ₂ )

0.2, and - forming an InGaN-based active region (123) extending along the semipolar crystal plane directly on the second layer (122). The method according to claim 12, wherein the formation of the first and second layers (121, 122) and the active region (123) occurs on a three-dimensional substrate (11) having a textured surface.